Since ExcelFinancialFunctions is not strong-signed, it cannot be loaded in .NET 4.7.2 framework.

[tonyqus]

I'm thinking rollback #1808

[tonyqus]

/oc is there any alternative solution to implement these Excel functions without ExcelFinancialFunctions library

[opencode-agent]

Yes — several viable options, given what the exploration shows (HEAD still has EFF wired into 14 files + FinancialAtpFunctions.cs; the rollback branch restores the old self-contained code):

Alternatives

#	Approach	Effort	Notes
1	Port from Apache POI	Medium	POI implements all financial functions natively in pure Java (org.apache.poi.ss.formula.functions). NPOI is a POI port — license-compatible (Apache 2.0), battle-tested, and matches existing code style. Best long-term fit.
2	Keep the rollback's pure-C# code and extend it	Low–Medium	Pre-#1808 NPOI already had Fv/Pv/Npv/Pmt/Nper/Irr/Mirr/Rate/IPMT/PPMT natively (main/SS/Formula/Functions/FinanceLib.cs:63, Irr.cs). Missing pieces: SLN/SYD/DB/DDB/VDB are trivial closed-form formulas (~15 lines each); PDURATION/RRI are one-liners. Bond/security functions (PRICE, YIELD, ACCRINT…) are the only hard part.
3	Vendor EFF's source as C#	Medium–High	ExcelFinancialFunctions is Apache 2.0 (port of Luca Bolognese's F# library) — its algorithms can be copied into NPOI directly, keeping full coverage without the assembly.
4	Strong-name a fork of EFF	Low	Recompile with your own SNK, publish as NPOI.ExcelFinancialFunctions. Fastest fix, but adds maintenance of a forked package.
5	TFM-conditional dependency	Low, ugly	<PackageReference Condition="'$(TargetFramework)' != 'net472'"> + #if NETFRAMEWORK fallbacks. Keeps two parallel implementations — not recommended.

Recommendation

Option 1 (+2): restore the rolled-back native implementations, then fill the remaining gaps by porting POI's Finance/FinanceFunction classes and its security-functions (Price, Yield, Accrint, coupon-date utils in org/apache/poi/ss/formula/functions/). That gives complete ATP coverage, zero external dependencies, strong-name compatibility on all TFMs, and stays consistent with how NPOI ports everything else. The ~35 ATP wrappers in FinancialAtpFunctions.cs would just swap EFF.Financial.* calls for the ported natives.

Want me to implement option 1/2 (restore native code + port the missing functions from POI)?

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